Cheap Web Space, Domain Name:
Web Space With E-Mail, PHP/MySQL.

Symptom

You have created a domain or subdomain. Common HTML page other static files such as images, CSS style sheets and JavaScript files can be opened without problems. However, PHP scripts always generate error 503 and do not display a result.

Cause

You have partially capitalized the domain or subdomain in the web space control panel, e.g. with an uppercase initial letter. This also affects file paths on the server. Linux is case-sensitive, but due to a bug that also exists in current versions of the Apache web server and PHP FPM service, PHP FPM expects all paths to be lowercase. Therefore, PHP cannot find the path to your website on the host, thereby not handling the called script. As a result, the web server receives no response and therefore displays the error 503 (service unavailable).

Solution

Delete the subdomain or domain and recreate it, but write all parts in lowercase letters. You can still reach the domain on the internet later in uppercase anyway. Only in the configuration on the host, it should be written in lowercase.

Overview of frequently asked questions